The present invention relates generally to a filtered lamp assembly useful in one form for illuminating aircraft cockpit instruments. More particularly, in a preferred embodiment thereof, the present invention provides a significantly improved infrared filtered lamp assembly having a wire form therein for sealing between a light bulb and a filter housing. Although the filtered lamp assembly of the present invention was developed for use with aircraft instruments, certain applications may be outside of this field.
Aircraft cockpit instruments, such as altimeters, compasses, and the like, are typically illuminated for low light flying conditions by a series of small incandescent bulbs mounted on the instrument panel adjacent to the instruments or are integrally contained within the instruments for which they provide light. The infrared light generated by an illumination system of this general type can seriously interfere with the use of night vision equipment, such as night vision goggles worn by pilots to detect infrared markings, even in total darkness, of targets and reference points on the ground. To alleviate this interference with night vision equipment, various types of infrared filter structures have been used in conjunction with light bulbs to shield the cockpit area from the infrared light that is inherently generated by hot filaments.
Prior designers of filtered lamp assemblies have typically used a lamp assembly of the type that is illustrated in FIGS. 1 and 2. This light assembly includes a hollow tubular housing (a), an incandescent light bulb (b) that is disposed within the housing (a), and a disc shaped member (c). The member (c) has the electrical leads (e) that extend from the incandescent bulb (b) threaded therethrough. The disc shaped member (c) fits tightly within the hollow tubular housing (a) to prevent the potting material (d) from leaking into the cavity formed between the light bulb (b) and the housing (a).
The prior techniques utilized to seal between the light bulb (b) and the filter housing (a) have a plurality of limitations. One such limitation is the difficulty and the associated added labor expense associated with threading the electrical leads (e) through a pair of bores (f) formed in the disc shaped member (c). A second limitation of the prior technique of using a disc shaped member (c) is that the degree of flexibility in positioning the electrical leads (e) within the housing (a) is limited by the placement of bores (f) in disc (c). A third limitation associated with using the disc shaped member is that the manufacturer must maintain a large inventory of these members (c) in order to correspond with the multitude of different sized housings that the light bulb (b) is positioned within. By having to maintain a quantity of different sizes members (c) there is an increase in complexity associated with assembling the filtered lamp assembly, and a significant cost increase to this process. A fourth limitation is that the disc (c) is, by itself, a costly part to produce because its size poses a number of manufacturing difficulties.
Even with the variety of earlier designs there remains a need for an improved filtered lamp assembly. The present invention satisfies this need in a novel and unobvious way.